MANHATTANVILLE COLLEGE Writing Assignment #4Chemical Composition of the Cell Membrane and its effect on Cell Processes Stephen Corvini 11/9/2011 Molecular Cell Biology Dr. Bettica
Stephen CorviniWriting Assignment 4Dr. BetticaNovember 8th, 2011 The cell membrane is one of the most important molecular components of the human body as itserves to protect the fundamental building block of life. It is composed of the substance cholesterol whichhas shown a correlation to cell proliferation (Siperstein, 1984). Recent research studies have shown thatthe enzyme 3-hydroxyl-3-methylglutaryl CoA (HMG-CoA) reductase works as a primary rate limitingenzyme for the synthesis of cholesterol (Siperstein, 1984). Organs such as the intestines have shown agreat amount of HMG-CoA and cholesterol because they require a great amount of cell proliferation(Siperstein, 1984). It is important to note that cholesterol is important in liver cells, especially in theprocess of hepatic regeneration. Cell cultures have shown that levels of cholesterol within cells willincrease approximately 24 hours before cells begin to enter the proliferation phase (Siperstein, 1984).Cholesterol is a steroid that is also well known for its ability to maintain the fluid nature of the cellmembrane as is described by the Fluid Mosaic Model. When compactin was introduced to a cell, levels ofproliferation were significantly lower. Cholesterol was shown to reverse the effects of this compoundwhich further verifies the role of this substance as a key player in cell proliferation (Siperstein, 1984).Although cell growth is a function of the cell membrane, the semi-permeable lipid based barrier containsvital proteins which allow it to communicate with the external environment and send signals via proteinpathways. The cell membrane contains a series of proteins embedded within the membrane that serve avariety of functions. Integrins are one specific class of proteins that play a key role in signaling and arewell known in the field of biology. These proteins possess a heterodimer structure that is composed ofboth alpha and beta subunits (Zhong and Rescorla, 2003). The function of integrins is to allowcommunication with the components of the extracellular matrix (ECM) in order to perform a variety offunctions (Zhong and Rescorla, 2003). Integrins play a crucial role in cell-ECM interactions which initiate
cell signaling. An example of pathway that provides a specific cell function is that of the PI3K/Aktpathway within the cell (Zhong and Rescorla, 2003). This pathway is vital as it blocks components thatwould otherwise signal the cell for receptor mediated apoptosis, or cell death. Integrin proteins bind withcomponents of the ECM in order to convert phosphatidylinositol-4,5-biphosphate (PIP2) intophosphatidylinositol-3,4,5-triphosphate (PIP3). This is successfully completed by the phosphorylation ofPIP2, thus converting it into PIP3 (Zhong and Rescorla, 2003). The significance of this pathway is thatthe molecule PIP3 blocks the binding of cell death signaling molecules such as Bad, NFkB, the receptorIkB, and Akt. All of these molecules are components which bind to signal a cell for apoptosis (Zhong andRescorla, 2003). Another form of interaction within the membrane is that of cell-cell adhesion. Cells that exhibit adhesion with other cells are capable of promoting cell survival by theconduction of specific signal pathways. This is seen in cells that exhibit cell-ECM pathways as previouslystated (Zhong and Rescorla, 2003). Research in colonial epithelial cells (CECs) has shown Neural CellAdhesion Molecules (NCAMs) are vital to the process of cell adhesion (Zhong and Rescorla, 2003). Thisis important because by carrying out the process of cell-cell adhesion the activity of β-catenin, Src-relatedkinases, and the function of the PI3K/Akt signal pathway are successfully maintained (Zhong andRescorla, 2003). This is important because this research provides evidence that if cells are not capable ofadhering to neighboring cells, the cells will be marked for apoptosis. It has also been noted that N-cadherin is utilized in the process of binding cells with adjacent neighbor cells (Zhong and Rescorla,2003). The cell membrane is vital to the survival of the cell in many ways and the transport of ions intoand out of the cell is essential to the cell’s homeostatic balance. The cell membrane contains a polar and non-polar region due the amphipathic nature ofphospholipids which are the primary component of the membrane bilayer. Molecules that possess noelectrical charge and are of the right molecular size are capable of being transported via the mechanism ofpassive transport. This is because they possess no charge difference to interfere with the overallelectrochemical state of the cell membrane (Szachowicz-Petelska et al, 2000). Some examples of
molecules that can pass through the membrane are ethanol, carbon dioxide and oxygen; all of which passthrough the membrane by means of simple diffusion (Szachowicz-Petelska et al, 2000). Althoughpassive diffusion allows molecules to move through there are channel proteins that are involved in theprocess which include ionotropic, metabotropic, and catalytic integral channel proteins (Szachowicz-Petelska et al, 2000). Within the membrane ionotropic proteins facilitates ions, metabotropic involve cellsignals, and catalytic are involved with enzyme facilitated reactions (Szachowicz-Petelska et al, 2000).Larger substances that possess an electrical charge such as sodium must pass through a pump that isfacilitated by the process of ATP-phosphorylation which results in a conformational change of thechannel protein in order to allow the charged molecule to pass through the membrane (Szachowicz-Petelska et al, 2000). There are several key carrier proteins that are involved in the facilitation of active diffusion whichinclude coupled carrier proteins, ATP pumps, and light driven pumps (Szachowicz-Petelska et al, 2000).Light driven pumps are only seen in bacterial organism cells (Szachowicz-Petelska et al, 2000). Channelproteins that undergo physical changes are necessary in order to allow the passage of certain syntheticmolecules into the cell as well. Recent research regarding drug transport mechanisms across the cellmembrane has shown evidence to suggest the employment of transport proteins aiding in the facilitationof drug molecules into the cell cytosol (Szachowicz-Petelska et al, 2000). Other research has shown thatabnormal changes in lipid structure can result in the occurrence of an abnormal amount of ion transferwithin the cell membrane (Vokurkova et al., 2005). Phagocytosis is an example of a key process that cancome into play as a result of substances that are transported into and out of the cell. The role of phagocytosis is the consumption or engulfment of cell matter that is targeted fordigestion within the body. An important instant of when phagocytosis becomes important is during thefunctioning of the immune system within the body. Macrophages are the most common cell types toperform the process of phagocytosis (Lennartz, 1999). Recent research has shown that phospholipasesmay be involved in the regulation of molecules that play a key role in the process of phagocytosis.
Among the molecules that are known to take part in phagocytosis are various kinases, GTP-bindingproteins, and specificially protein kinase C (Lennartz, 1999). Polymerization of actin filaments within thecell membrane combine with membrane movement have also been shown to be important to theengulfment of particulate matter by components of the cell membrane (Lennartz, 1999). It has been seenthat phospholipases act as generators for secondary messengers. Important phospholipases that contributeto this process are phospholipase C, phospholipase D, and phosphoinositide 3-OH kinase (PI(3)K)(Lennartz, 1999). These phospholipases help with Immunoglobin binding in cell as well (Lennartz, 1999).There are many important cell components that are vital to this process within the membrane. The cell membrane is perhaps one of the most simply constructed components of the cell, but itexhibits a high level of intricate functionality. All fields of biology acknowledge the importance of thiscrucial component of the cell’s foundation. The many proteins and molecules which are embedded withinthe membrane assist this structure in its function. The cell membrane takes part in processes such as cellgrowth, transport, signaling, preservation, and phagocytosis.
Works CitedMichelle R. L. 1999. Phospholipases and phagocytosis: The role of phospholipid-derived second messengers in phagocytosis. Int J Biochem Cell Biol 31(3-4):415-30.Siperstein, Marvin. "Role of Cholesterogenesis and Isoprenoid Synthesis in DNA Replication." Journal of Lipid Research 25 (1984): 1462-468. 5 Nov. 2005. Web. 3 Nov. 2011. <http://www.jlr.org/content/25/13/1462.full.pdf+html>.Szachowicz-Petelska B, Figaszewski Z, Lewandowski W. 2001. Mechanisms of transport across cell membranes of complexes contained in antitumour drugs. Int J Pharm 222(2):169-82.Vokurková M, Nováková O, Dobes˘ová Z, Kunes˘ J, Zicha J. 2005. Relationships between membrane lipids and ion transport in red blood cells of dahl rats. Life Sci 77(13):1452-64.Zhong X and Rescorla FJ. Cell surface adhesion molecules and adhesion-initiated signaling: Understanding of anoikis resistance mechanisms and therapeutic opportunities. Cell Signal (0).